Survivors of hematologic malignancies remain at risk of disease relapse. Though allogeneic hematopoietic cell transplant (alloHCT) in appropriately selected survivors saves lives, at least 20% of alloHCT recipients die of transplant-related causes and many others experience persistent deficits in health-related quality of life. Pre-transplant physical fitness predicts outcomes following alloHCT, but no evidence exists for pre-alloHCT fitness interventions that might mitigate the effects of post-alloHCT toxicity and physiologic stress. Thus, there is an urgent need to develop interventions that improve the physical fitness of cancer survivors preparing to undergo alloHCT and to test the intervention effects on post-alloHCT outcomes. Continued existence of this need represents an important problem because many individuals cured of disease post-alloHCT continue to experience adverse outcomes. Our long- term goal is to reduce mortality and disability following alloHCT. The overall objective of this R21 application is to test the effects of pre-alloHCT exercise interventions [interval exercise training (IET); brief high intensity periods of exercise at 75-95% of maximum heart rate, and viewable accelerometry (VA)] upon pre- and post-alloHCT fitness biomarkers. The rationale for this research is that the results will enable a larger trial of this intervention at the R01 level. This research study will pursue two specific aims: (1) assess the feasibility of a trial to test the effects of pre-alloHCT IET plus VA upon transplant readiness; (2 determine the impact of pre-alloHCT IET plus VA on prognostic pre-alloHCT biomarkers of fitness and early post-alloHCT markers of toxicity. To test these aims, we will conduct a trial assigning participants to one of two arms: pre-alloHCT IETplus VA (N=30) or encouragement to exercise with non-viewable accelerometry (N=30). For the second aim, markers of cellular aging (p16INK4a expression) and physical performance (VO2peak and 6 minute walking distance) will be used to assess the effects of pre-alloHCT exercise on pre-alloHCT fitness, and post-alloHCT symptom burden and hospitalization length will be used to assess the effects of pre-alloHCT exercise on early post-alloHCT toxicity. This project is innovative in that it pilots a novel pre-alloHCT trial of high-intensity exercise and motivation, and quantifies the impact of this intervention using under-explored but promising measurements and scales. The proposed research is significant because the results may lead to a follow-on R01 application with the potential to decrease morbidity and mortality among patients undergoing alloHCT.